1. Field of the Invention
The present invention relates to a mounting structure of a high-frequency wiring board which transmits high-frequency signals in a millimeter waveband of 30 GHz or more, and more particularly relates to a mounting structure of a high-frequency wiring board in which transmission characteristics of high-frequency-signals of a connecting section to an external electric circuit board are improved.
2. Description of the Related Art
Up to now, as a mounting structure of a high-frequency wiring board which transmits high-frequency signals, a type of using a lead terminal for electric connection to an external electric circuit board has been mainstream. However, in order to decrease a transmission loss at a connecting section for high-frequency signals which have become higher, it becomes necessary to shorten the length of a connecting section to an external electric circuit board. Accordingly, adoption of a package of chip scale package (CSP) type or ball grid array (BGA) type has been pursued, which are surface mounting types of mounting an electrode pad on the lower face of a high-frequency wiring board in place of a lead terminal and connecting the electrode pad to a connecting pad on the upper face of an external electric circuit board by the use of a conductive connecting member such as solder.
A high-frequency wiring board which has a mounting structure of such a surface mounting type comprises, for example, an insulation board made of aluminum oxide sintered compact, glass ceramics sintered compact or the like and a wiring conductor made of a metallic material such as tungsten or copper. By mounting a high-frequency semiconductor element on the upper face and/or lower face of the high-frequency wiring board by the use of a wire bonding mounting method, a flip chip mounting method or the like and electrically connecting the wiring conductor of the high-frequency wiring board and an electrode of the high-frequency semiconductor element, a semiconductor device is constituted.
This high-frequency wiring board has a wiring conductor inside. The wiring conductor is placed from a high-frequency semiconductor element electrode pad formed on the upper face and/or lower face of the high-frequency wiring board to an electrode pad formed on the lower face of the high-frequency wiring board. Then, the electrode pad formed on the lower face of the high-frequency wiring board is physically and electrically joined to a connecting pad of an external electric circuit board by the use of a conductive connecting member, whereby this semiconductor device is mounted on the external electric circuit board.
In this mounting structure of a high-frequency wiring board, normally, in order to ensure stable electric conduction and ensure stable physical connection as well, an electrode pad and a conductive connecting member which have as large a diameter as possible are needed. The size relates to a space between electrode pads specified by the size of a high-frequency wiring board and the number of the electrode pads, that is, a space between a conductive connecting member connected to a high-frequency signal electrode pad and a conductive connecting member connected to a ground electrode pad adjacent thereto. In general, in a case where a space between electrode pads is 1.0 mm, the diameter of an electrode pad is 0.7 mm and the diameter of a conductive connecting member in a section parallel to the lower face of a high-frequency wiring board is 0.8 mm. Furthermore, in a case where a space between electrode pads is 0.8 mm, the diameter of an electrode pad is 0.5 mm and the diameter of a conductive connecting member in a section parallel to the lower face of a high-frequency wiring board is 0.6 mm.
So far, it has been mainstream that a frequency in a high-frequency semiconductor element is less than 10 GHz. However, in recent years, as a high-frequency semiconductor element has a faster working speed and uses a higher frequency, such a mounting structure of a high-frequency wiring board that efficiently transmits high-frequency signals of 10 GHz or more is demanded.
By contrast, the above-described conventional mounting structure of a high-frequency wiring board has a problem that impedance drastically changes owing to high stray capacity between a ground layer which a high-frequency wiring board has inside and an electrode pad on the surface, and consequently the transmission characteristic deteriorates significantly as the frequency becomes higher.
Therefore, as a technique of decreasing stray capacity in a mounting section of a high-frequency wiring board, a technique of decreasing stray capacity and improving the transmission characteristic by downsizing an electrode pad is proposed (Japanese Unexamined Patent Publication JP-A 9-306917 (1997)), for example.
However, the above-described conventional mounting structure of a high-frequency wiring board has a problem that in the case of downsizing only an electrode pad, impedance changes owing to stray capacity between a conductive connecting member and a ground layer, and consequently as the frequency becomes higher, transmission characteristics deteriorate, and especially transmission characteristics of high-frequency signals in a millimeter waveband of 30 GHz or more deteriorate.
Further, in the case of downsizing a conductive connecting member to decrease stray capacity between the conductive connecting member and a ground layer, there is a problem that in a direction along a section of the conductive connecting member parallel to the lower face of a high-frequency wiring board, induction components significantly increase and impedance drastically changes, and consequently as the frequency becomes higher, transmission characteristics deteriorate and especially transmission characteristics of high-frequency signals in a millimeter waveband of 30 GHz or more deteriorates.
The present invention was thought in view of the problems of the conventional techniques described above, and an object of the invention is to provide a mounting structure of a high-frequency wiring board which can transmit high-frequency signals in a millimeter waveband of 30 GHz or more at a connecting section between a high-frequency wiring board and an external electric circuit board, the high-frequency wiring board being mounted on the external electric circuit board via a conductive connecting member.
The invention is a mounting structure of a high-frequency wiring board comprising: a high-frequency wiring board; a high-frequency semiconductor element mounted on an upper face and/or lower face thereof; an external electric circuit board; a plurality of electrode pads formed on the lower face of the high frequency wiring board; a plurality of connecting pads formed on an upper face of the external electric circuit board; and conductive connecting members for connecting the plurality of electrode pads formed on the lower face of the high frequency wiring board and the plurality of electrode pads formed on the upper face of the external electric circuit board so as to be opposed to each other, wherein A/Bxe2x89xa72 is satisfied, where A is a pitch between a conductive connecting member connected to a high-frequency signal electrode pad and a conductive connecting member connected to a ground electrode pad adjacent thereto, and B is a maximum diameter of the conductive connecting members in sections parallel to the lower face of the high-frequency wiring board, and wherein a space L1 between the lower face of the high-frequency wiring board and the upper face of the external electric circuit board is one sixteenth or less of a wavelength of high-frequency signals processed by the high-frequency semiconductor element.
According to the invention, the above constitution makes it possible to decrease stray capacity between the conductive connecting member and a ground layer formed inside the high-frequency wiring board, and also makes it possible to decrease induction components in a direction along a section of the conductive connecting member parallel to the lower face of the high-frequency wiring board. As a result, an impedance change is small, and good transmission characteristics of high-frequency signals can be realized.
Further, in the above constitution, it is preferable that a transmission line drawn out of a high-frequency signal connecting pad is formed on the upper face of the external electric circuit board, and a length of the high-frequency wiring board overlapping on the transmission line is one half or less of the wavelength of the high-frequency signals.
According to the invention, it is possible to inhibit a change of impedance and radiation of electromagnetic waves due to electromagnetic field interference between the transmission line on the upper face of the external electric circuit board and the high-frequency wiring board. As a result, better transmission characteristics of high-frequency signals can be realized.
According to the invention, it is possible to provide a mounting structure of a high-frequency wiring board which can transmit high-frequency signals in a millimeter waveband of 30 GHz or more at a connecting section between a high-frequency wiring board and an external electric circuit board, the high-frequency wiring board being mounted on the external electric circuit board via conductive connecting members.
The invention is a mounting structure of a high-frequency wiring board in which a high-frequency wiring board equipped with a high-frequency semiconductor element on the upper face and/or lower face thereof and provided with a plurality of electrode pads formed on the lower face thereof which electrode pads electrically connected to electrodes of the high-frequency semiconductor element, is disposed on an external electric circuit board provided with a plurality of connecting pads formed on the upper face thereof which connecting pads are associated with the electrode pads and the plurality of electrode pads and the plurality of connecting pads are connected via conductive connecting members so as to be opposed to each other, the mounting structure of a high-frequency wiring board being characterized in that A/Bxe2x89xa72 is satisfied wherein A is a pitch between a conductive connecting member connected to an electrode pad for high frequency signals of the electrode pads and a conductive connecting member connected to a ground electrode pad adjacent thereto, and B is a maximum diameter of the conductive connecting members in sections parallel to the lower face of the high-frequency wiring board, and a space between the lower face of the high-frequency wiring board and the upper face of the external electric circuit board is one sixteenth or less of a wavelength of high-frequency signals processed by the high-frequency semiconductor element.
In the invention it is preferable that a transmission line drawn out of a connecting pad for high frequency signals of the connecting pads is formed on the upper face of the external electric circuit board, and a length of the high-frequency wiring board overlapping on the transmission line is one half or less of the wavelength of the high-frequency signals.
In the invention it is preferable that a frequency range of the high-frequency signals is 30 GHz or more.
The invention is a mounting structure of a high-frequency wiring board, comprising:
a high-frequency semiconductor element having a plurality of electrodes, for processing high-frequency signals of a predetermined wavelength;
an insulation board on which the high-frequency semiconductor element is mounted;
a plurality of electrode pads formed on one surface of the insulation board, the plurality of electrodes being electrically connected to the electrodes of the high-frequency semiconductor element, and including at least a high-frequency electrode pad and a ground electrode pad adjacent thereto;
an external electric circuit board on which the insulation board with the high-frequency semiconductor element mounted thereon is mounted;
a plurality of connecting pads which are formed on one surface of the external electric circuit board which one surface is opposed to the one surface of the insulation board, the plurality of connecting pads being arranged so as to correspond to an arrangement of the plurality of electrode pads, and including at least a high-frequency connecting pad and a ground pad adjacent thereto; and
a plurality of conductive connecting members for electrically connecting the plurality of electrode pads with the plural connecting pads,
wherein a first conductive connecting member connected to the high-frequency signal electrode pad and a second conductive connecting member connected to the ground electrode pad adjacent thereto have a pitch A;
wherein a maximum diameter B of these first and second conductive connecting members in sections parallel to the one surface of the insulation board is selected so as to be one half or less of the pitch A (A/Bxe2x89xa72); and
wherein a space L1 between the one surface of the insulation board and the one surface of the external electric circuit board is selected so as to be one sixteenth or less of the wavelength of the high-frequency signals processed by the high-frequency semiconductor element.